Datex-Ohmeda S/5 M-ESTPR, Technical Reference Manual Slot

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Datex-Ohmeda S/5 monitors
Document No. 800 1008-2
20
Temperature measurement unit
Value of NTC-resistor in the probe depends on patient’s temperature. It is measured with the
following principle.
The temperature signal(s) is produced by voltage dividers, part of which is the patient probe (YSI
400-series thermistor). The output is amplified by the calibrated amplifier(s) whose offset voltage
makes its output spread on both sides of zero. Wider output range (measurement range) means
better resolution.
NTC
to AD
converter
+5Vreference
offset
A1
0 °C => 7K357
15 °C => 3K541
25 °C => 2K253
38 °C => 1K301
45 °C => 984R1
Figure 9 Temperature measurement principle
Invasive blood pressure measurement unit
Is5 V voltage is supplied to the pressure transducer. From the bridge connection a
differential voltage, which depends on pressure and supplied voltage, is calculated (see the
formula below).
U
out
= U
in
×
pressure
×
5 V, where U
in
is 5 V
Þ
U
out
= 25 V
×
pressure [mmHg]
Pressure amplification is realized in the instrumentation amplifier. Gain of the amplifier is set so
that the level of the signal transferred to A/D converter stays within the measurement range even
when there are circumstantial offsets or offsets caused by the transducer. There is a filter before the
amplifier to attenuate high frequency disturbances.
Input
Filter
Instrumentation
amplifier
to AD converter
Pressure
transducer
Vin
Vout
G
Figure 10 Pressure measurement principle